1. Field of the Invention
The present invention relates to a pneumatic tire which can suppress cracks caused by a ribbon interface of a sidewall outer peripheral wall, and which does not deteriorate the productivity, and to a producing method of such a pneumatic tire.
2. Description of the Related Art
An example of common producing methods of a pneumatic tire is as follows. First, a cylindrical forming drum is prepared, and an inner linear rubber member and a carcass ply having predetermined width are disposed cylindrically on outer peripheries thereof. Then, annular beads are fitted over both sides of the carcass ply in its widthwise direction, the end of the carcass ply in the widthwise direction is wound back outside and then, a sidewall rubber member is disposed on the side of the outer periphery of the wound back ply, thereby forming a first case. Next, the first case is disposed on the side of an inner periphery of a cylindrical second case formed, in a different step, from a belt member and a tread rubber member, a central portion is swelled and deformed while approaching a pair of beads, thereby crimping an outer peripheral surface of the first case onto an inner peripheral surface of the second case, thereby forming a green tire. Such a producing method is disclosed in Japanese Patent Application Laid-open No. H06-254990.
Conventionally, there is a known ribbon winding method as a method for forming a rubber member. According to the ribbon winding method, a narrow rubber ribbon made of unvulcanized rubber composition is wound along the circumferential direction of the tire to form a rubber member of a predetermined cross section shape. With this method, it is possible to precisely and easily form a sidewall rubber 30 for a pneumatic tire as shown in FIG. 5. Japanese Patent Application Laid-open No. 2002-200677 discloses a method for forming a sidewall rubber by winding a narrow rubber ribbon around an outer side of a carcass ply deformed toroidally to form the sidewall rubber.
However, when the sidewall rubber is formed by the ribbon winding method, a difference in level is caused in a sidewall outer peripheral wall along a ribbon interface of thereof, and there is a problem that a crack is generated due to this. Especially when the height of tire cross section was 110 mm or less, it was found that a large distortion was applied to a region of maximum width position from a shoulder portion when a load rolls at the time of running, and a crack was prone to be generated.
To cope with this problem, it is conceived that the difference in level on a sidewall outer peripheral wall is reduced by using a narrower rubber ribbon. However, according to this method, since the number of windings of the rubber ribbon is largely increased, the forming time is increased and the productivity is deteriorated. In Japanese Patent Application Laid-open No. 2004-50985, there is proposed a pneumatic tire in which a sidewall outer peripheral wall in a region where a crack is prone to be generated is coated with a rubber sheet. In this case, there are a problem that peeling off is generated due to air accumulated between the rubber sheet and the outer peripheral wall, and a problem that the productivity is deteriorated because of the paste of the rubber sheet.